prov:value
| - preferably each R3 is identical and is a fluorine, chlorine or bromine, atom, a C1???C4 alkyl group which may be halogenated, a C6???C8 aryl group which may be halogenated, a ???NR???2, ???SR???, ???OR???, ???OSiR???3 or ???PR???2 radical, wherein R??? is one of a chlorine atom, a C1???C4 alkyl group, or a C6???C8 aryl group;
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